1. Field of the Invention
The invention relates to wafer positioning systems, and in particular to an on-line wafer positioning system having signal receiver to detect wafer position.
2. Brief Discussion of the Related Art
Semiconductor manufacturing processes include processes such as oxidation, diffusion, lithography, etching, CVD, and others. To integrate related processes in a single system and process and transfer wafers quickly in a vacuum environment avoiding contamination, automatic semiconductor manufacturing equipment is critical.
Multi-process chambers require less space, have a shortened production period, and consume less vacuum system resources. A general multi-process chamber design, as shown in FIG. 1, comprises a front end wafer handling chamber 14 connecting the transfer system of the factory and transferring wafer carriers to a load lock chamber 16 via robots 18. Further, a wafer handling chamber 20 is disposed in the center of the machine, in which a wafer transfer apparatus 22 is disposed and further comprises a wafer transfer robot 28. Outside the wafer handling chamber 20, a plurality of processing chambers 24 and cooling chambers 25 are disposed to load/unload wafers. The wafer transfer robot 28 is controlled by optical detection through a position point 32 of a position stage 34 (only partially shown). Moreover, through the wafer transfer robot 28, wafers 30 can be moved from the load lock chamber 16 to the processing chambers 24 to execute various processes or from the processing chambers 24 to the cooling chambers 25 to be cooled.
Wafers 30 are supported by a tray 26 and move between processing chambers 24 by the wafer transfer robot 28 in the wafer handling chamber 20. Due to mechanical loss, the wafer transfer robot 28, however, may cause displacement of the wafer position and is incapable of accurate, wafer positioning in the processing chambers. Such displacement may create process instability and malfunction of the vacuum clamp head. Due to the vacuum state of the wafer handling chamber, the machine must stop product processing and break vacuum to conduct the maintenance, interrupting production and possibly damaging wafers. Furthermore, if horizontally mis-positioned, the wafer transfer robot 28 may lose horizontal stability, thus generating vibration, further damaging wafers and the wafer carrier.
U.S. Pat. No. 6,275,297 discloses a system and method of wafer position detection on a wafer transfer robot. A transparent area is disposed above the transfer channel between the wafer handling chamber and the processing chamber. Utilizing an optical sensor and a reflective device disposed on the wafer transfer robot to determine the distance between the wafer and the edge of the tray of the wafer transfer robot, wafer position accuracy can be determined. In a conventional system, however, only relative wafer position can be detected.